Malignant schwannoma: a light microscopic and ultrastructural study.

The light microscopic and ultrastructural features of 3 cases of malignant schwannoma were studied and compared with those of other types of soft-tissue sarcoma. The tumor in 1 of these cases originated in an intercostal nerve and was composed of compactly arranged spindle-shaped tumor cells. The other 2 cases showed osteogenic areas in addition to exhibiting prominent nuclear palisading, focal myxoid changes, and a rosette-like arrangement of tumor cells. The tumor in 1 of these latter cases occurred at the site of a preexisting neurofibroma. The Schwann cell origin of these tumors is strongly supported by the ultrastructural findings of basement membranes and conspicuous intercellular junctions in all 3 cases and dense-core granules in 1.